Tcf1 and Lef1 transcription factors underpin the inception of T cell fate

The goal of this study is to resolve the heterogeneity of transcriptomic and chromatin accessibility (ChrAcc) landscape in DN1 thymocytes harboring ETPs. Comparison of molecular features between ETPs with non-ETP DN1 cells predicted contribution by Tcf/Lef family transcription factors, and pre-thymic ablation of Tcf1 and Lef1 impaired ETP formation. Single cell analysis of the factor-targeted ETPs revealed that they converged on Notch1 or Notch pathway effector molecules including Hes1 and Hhex, to support their transcriptional activation. Bone marrow (BM) LSK cells were sorted from CreER+ WT or CreER+ Tcf7-floxed, Lef1-floxed mice and seeded on OP9-DL1 monolayers for culture. The cells were treated with 4-OH tamoxifen during days 3-5 culture and cKit+ DN1 cells were sorted on day 7 of culture for bulk RNA-seq and ATAC-seq analysis.